The present invention relates to an image processing method and apparatus for displaying a visible image.
In recent years, many image processing apparatuses that can display digital images on display devices have been proposed. For example, a copying machine with a preview function, a personal computer with a scanner, and the like have been proposed. In apparatuses of this type, a color image immediately before hard copy output can be displayed on a display device as a preview image.
In order to make the color tone of the preview image match that of the original image, the monitor characteristics (gamma characteristics, color reproduction characteristics, color temperature) must be detected. Also, as one problem associated with the visual sense characteristics, the color perceived changes when illumination light changes (color adaptation). For this reason, the type of illumination light must be detected. For this purpose, the color temperature and type of a monitor, the type of a fluorescent lamp used in illumination, or the like, and the image density (the gamma value of the monitor) can be selected from a console, so as to adjust the color tone of the preview image displayed on the monitor to become closest to that of the original image.
The visual sense of a human being is strongly influenced by the background colors. For example, as is well known, when two identical colors are placed on different background colors upon observation, they are recognized as different colors. However, the prior art does not consider any such visual sense characteristics of a human being associated with the background colors, and simply displays a preview image on a full display range of the display device. For this reason, it is hard to make the color tone of the preview image perfectly match that of the original image. For example, when white as the background color of an original read using a scanner is displayed using a color adaptation predictive method, the background of the original appears tinged with yellow.
On the other hand, using a 4 (rows)xc3x978 (columns) masking/UCR matrix, masking processing and undercolor removal processing normally include a nonlinear calculation, which is described as:                               (                                                    C1                                                                    M1                                                                    Y1                                                                    K1                                              )                =                              (                                                            a11                                                  a12                                                  a13                                                  a14                                                  a15                                                  a16                                                  a17                                                  a18                                                                              a21                                                  a22                                                  a23                                                  a24                                                  a25                                                  a26                                                  a27                                                  a28                                                                              a31                                                  a32                                                  a33                                                  a34                                                  a35                                                  a36                                                  a37                                                  a38                                                                              a41                                                  a42                                                  a43                                                  a44                                                  a45                                                  a46                                                  a47                                                  a48                                                      )                    ⁢                      (                                                            C0                                                                              M0                                                                              Y0                                                                              K0                                                                                                  K0                    ·                    K0                                                                                                                    C0                    ·                    M0                                                                                                                    M0                    ·                    Y0                                                                                                                    Y0                    ·                    C0                                                                        )                                              (        1        )            
Upon displaying a preview image, an inverse calculation (inverse masking processing) of such nonlinear calculation must be done. In such nonlinear calculation, it is normally impossible to analytically obtain its inverse conversion. In addition, high-order nonlinear terms are generated by overflow or underflow that occurs since data are limited to a range from 0 to 25, in addition to second-order nonlinear terms of the masking/UCR matrix in the masking processing, thus making the calculation of the inverse conversion harder. For this reason, conventionally, the calculation coefficients of the inverse masking processing are obtained by calculating a 4 (rows)xc3x974 (columns) masking/UCR matrix and calculating its inverse matrix in addition to the masking/UCR matrix actually used in the masking processing and undercolor removal prooessing.
However, the 4xc3x974 masking/UCR matrix suffers larger conversion errors (color differences) than the 4xc3x978 masking/UCR matrix, and with the prior art that obtains an inverse masking matrix using the 4xc3x974 masking/UCR matrix, the color tone of the preview image appears different from that of the original image depending on the types of colors to be displayed.
Furthermore, the gamma characteristics of a display device normally have a nonlinear relationship between the input and output luminances. To correct such nonlinearity, gamma correction is done. However, when the nonlinearity of the display device is strong, the gamma correction results in discrete data, and the gradation characteristics of the image are lost. As a result, pseudo edges are likely to be generated.
The present invention has been made in consideration of the above-mentioned problems and has as its object to provide an image processing method and apparatus, which display a background for a display image, and allow the user to freely set the background color so as to satisfactorily reproduce the color tone of the display image.
It is another object of the present invention to provide an image processing method and apparatus, which can automatically and appropriately set the background color of a display image on the basis of the display condition of the display image and illumination light, and can appropriately reproduce, especially, the color tone of a preview image.
It is still another object of the present invention to provide an image processing method and apparatus, which can appropriately reproduce the color tone of a preview image by adjusting the background color of a display image to the color of a frame of a display device that is to display the display image.
It is still another object of the present invention to provide an image processing method and apparatus, which can reduce conversion errors in inverse masking processing, and can improve the color reproducibility of a preview image.
It is still another object of the present invention to provide an image processing method and apparatus, which optimize conversion coefficients by obtaining a color difference before and after inverse masking processing using a plurality of color data prepared in advance, and determining the conversion coefficient to minimize the color difference, thereby reducing conversion errors in the inverse masking processing.
It is still another object of the present invention to provide an image processing method and apparatus, which can prevent data from becoming discrete due to gamma correction, and can prevent deterioration of image quality.
In order to achieve the above objects, according to one aspect of the present invention, there is provided an image processing method for generating image data representing a display image on the basis of input image data, comprising: the input step of inputting a display condition for the display image and information associated with illumination light; the setting step of automatically setting a background color on the basis of the display condition for the display image and the information associated with illumination light input in the input step; and the display step of displaying the background color set in the setting step as a background of the display image.
Other features and advantages of the present invention will be apparent from the following descriptions taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.